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Re: [PATCH 16/21] parallels: naive implementation of allocate_clusters w


From: Alexander Ivanov
Subject: Re: [PATCH 16/21] parallels: naive implementation of allocate_clusters with used bitmap
Date: Mon, 18 Sep 2023 15:18:20 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.15.1



On 9/18/23 15:14, Denis V. Lunev wrote:
On 9/18/23 15:09, Alexander Ivanov wrote:


On 9/15/23 20:41, Denis V. Lunev wrote:
The access to the bitmap is not optimized completely.

Signed-off-by: Denis V. Lunev <den@openvz.org>
---
  block/parallels.c | 51 ++++++++++++++++++++++++++++++++++++-----------
  1 file changed, 39 insertions(+), 12 deletions(-)

diff --git a/block/parallels.c b/block/parallels.c
index a6d2f05863..2efa578e21 100644
--- a/block/parallels.c
+++ b/block/parallels.c
@@ -253,7 +253,7 @@ allocate_clusters(BlockDriverState *bs, int64_t sector_num,
  {
      int ret = 0;
      BDRVParallelsState *s = bs->opaque;
-    int64_t pos, space, idx, to_allocate, i, len;
+    int64_t i, pos, idx, to_allocate, first_free, host_off;
        pos = block_status(s, sector_num, nb_sectors, pnum);
      if (pos > 0) {
@@ -276,15 +276,13 @@ allocate_clusters(BlockDriverState *bs, int64_t sector_num,
       */
      assert(idx < s->bat_size && idx + to_allocate <= s->bat_size);
  -    space = to_allocate * s->tracks;
-    len = bdrv_co_getlength(bs->file->bs);
-    if (len < 0) {
-        return len;
-    }
-    if (s->data_end + space > (len >> BDRV_SECTOR_BITS)) {
+    first_free = find_first_zero_bit(s->used_bmap, s->used_bmap_size);
+    if (first_free == s->used_bmap_size) {
          uint32_t new_usedsize;
+        int64_t space = to_allocate * s->tracks + s->prealloc_size;
+
+        host_off = s->data_end * BDRV_SECTOR_SIZE;
  -        space += s->prealloc_size;
          /*
           * We require the expanded size to read back as zero. If the
           * user permitted truncation, we try that; but if it fails, we @@ -313,6 +311,32 @@ allocate_clusters(BlockDriverState *bs, int64_t sector_num,           s->used_bmap = bitmap_zero_extend(s->used_bmap, s->used_bmap_size,
                                            new_usedsize);
          s->used_bmap_size = new_usedsize;
+    } else {
+        int64_t next_used;
+        next_used = find_next_bit(s->used_bmap, s->used_bmap_size, first_free);
+
+        /* Not enough continuous clusters in the middle, adjust the size */
+        if (next_used - first_free < to_allocate) {
+            to_allocate = next_used - first_free;
+            *pnum = (idx + to_allocate) * s->tracks - sector_num;
It looks, we can write this simplier:
    *pnum = to_allocate * s->tracks;
because idx and sector_num aren't changed from idx calculation:
    idx = sector_num / s->tracks;

absolutely NO! sector_num can be unaligned. Here we get to the
situation when the end of the operation is aligned to cluster
and is calculated above.

Den

OK, now I got the idea.

Reviewed-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>




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